This invention relates to an electronic device provided with recording unit in which liquid is made to generate air bubbles by the action of thermal energy and the liquid is made to discharge by the operating force based on the change in the phase of the air bubbles. Further, this invention offers an electronic device capable of representing dense and light print density such as half tone by controlling the number of times of discharge.
In the conventional so called thermal print system where thermal head is made to touch heat sensitive paper to develop color, the time required for the chemical changes for color development on the heat sensitive paper is comparatively long. Therefore in order to repeat electric trasmission a plural number of times such as two times or three times, that much more time is required and as a result it was difficult to repeat a plural times while securing practically necessary printing speed. Moreover, high density was not always obtained by leaving the head pressed at the same position of the heat sensitive paper and transmitting electricity a plural number of times.
In the thermal ink jet system according to this invention, however, since the air bubbles are generated at high speed by heat generation, resultant practical printing speed is not damaged by repeating air bubbles generation many times and discharging the ink many times.
Moreover, since by discharging ink many times to the same position of the printing paper the amount of ink injected to the point of the printing paper is increased, the dot diameter caused by running ink is increased and becomes dense, the large contrast effect of the print is obtained.
Moreover, in the conventional ink jet system, for example, the system in which piezo electric element is used and ink is discharged by the mechanical distortion of ink leading tube, it was hard to obtain contrast of print by large number of times of discharge of ink for reason of limitation caused by response speed of the mechanical distortion and for the following reasons.
For constructional reason of establishing piezo electric elements around the lead-out tube, it was hard to arrange a large number of the lead-out tubes so close to one another as the proper character dot pitches. Accordingly, the method in which many dots are discharged by moving a small number of lead-out tubes mechanically in the vertical or horizontal direction of the character was employed in many cases. In this case, time is naturally required in the mechanical shifting and operation.
Therefore, it was necessary to end this movement and stopping in smallest possible time in order to obtain required printing speed. However, there is limit in machine speed. For this reason, it was difficult to perform a large number of times of ink discharge without sacrificing practical printing speed.
On the contrary, in the thermal ink jet system according to this invention, since its contruction is so simple as to fill a large number of grooves provided on one surface of the base board with ink and to give thermal energy selectively corresponding to the grooves, recording can be made as close to each other as the same degree of the dot pitches of practical character similar to the thermal head for conventional heat sensitive paper.
Accordingly, by employing such a multi-head configuration as this, mechanical driving of the head becomes unnecessary and improvement of printing speed is attained without adding the time required in the mechanical driving.
Moreover, a large number of times of ink discharge can be made within the range of practical printing speed.
Furthermore, the number of liquid drops discharged at the same time can also be controlled easily.